A push type driving belt to be used in a belt type continuously variable transmission is known in the prior art. The driving belt of this kind is formed by annularly juxtaposing a plurality of plate member called an “element” or a “block” in a same orientation, and by fastening the juxtaposing plate members by an annular member such as a band, a hoop and a ring (as will be called a “ring” hereinafter). Both side faces of the element are inclined in accordance with an inclination of a V-groove formed between sheaves of a pulley to have a V-shaped cross-section or a trapezoidal cross-section. The side faces of the element thus inclined are contacted individually with an outer face of the V-groove to serve as a flank face when the element enters into the V-groove. Therefore, in a V-belt thus structured, power is transmitted frictionally between the pulley and the ring by a wedge action between the outer face of the V-groove of the pulley and the flank face of the element.
One example of the above-explained V-belt is disclosed in Japanese Patent Laid-Open No. 1-65347. According to the V-belt taught by Japanese Patent Laid-Open No. 1-65347, a transverse element (i.e., an element) of general trapezoidal shape is formed with a base and fins slanted with respect to the base. A plurality of the transverse elements thus formed are joined together by an elastomer mass through a longitudinal reinforcement(s).
According to the example taught by Japanese Patent Laid-Open No. 1-65347, an angle of lateral sides of inner edge of each transverse element (i.e., the flank face) is slightly greater than a slant angle of interior walls of pulleys (i.e., opening angle of the V-groove).
Therefore, according to the teachings of Japanese Patent Laid-Open No. 1-65347, a recess opening toward an outer circumferential side is formed at the width center of the transverse element. In case of applying the V-belt using this kind of the elements to the belt type continuously variable transmission, a radial load is applied to the element by a tension of the ring and a clamping force is applied to the element by the pulley, under the situation in which the V-belt is pushed by a thrust force of the pulley to drive the continuously variable transmission. In this situation, the element is compressed elastically widthwise. As a result, an angle between the flank faces is reduced to be narrower than an initial angle, and a contact point between the flank face and the outer face of the V-groove is displaced toward inner circumferential side from an initial contact point. Consequently, the elements are off-balanced in the pulley, and a torque capacity between the pulley and the V-belt is thereby degraded. Moreover, durability of the V-belt may be deteriorated. In order to avoid the above-explained disadvantages, according to the transverse element taught by Japanese Patent Laid-Open No. 1-65347, the angle between the flank faces of the transverse element is widened to be slightly greater than an open angle of the V-groove of the pulley.
However, if the angle between the flank faces is thus wider than the open angle of the V-groove, the element is to be clamped by the pulley unevenly only at its upper portion (i.e., at the outer circumferential side) until the angle between the flank faces becomes congruent with the open angle of the V-groove as a result of elastic deformation. In this situation, columns protruding from side ends of the element toward the outer circumferential side on which the flank face is formed individually are subjected to a bending moment to be bent inwardly (i.e., toward the width center). As a result, durability of the element, that is, durability of the V-belt is deteriorated. Therefore, the conventional V-belt has to be improved to enhance its durability.